Heating, ventilating and air conditioning (HVAC) systems for automotive vehicles sometimes employ multi-zone ducting and controls to permit individual comfort control. For example, the driver side and the passenger side of the front of the compartment comprise separate zones and separate temperature controls so that, within limits, the temperature of one side can be different from the other side according to occupant preferences. Other multi-zone systems comprise separate ducts for driver side and passenger side in the front and either one or two zones for rear seat passengers.
Heretofore the multi-zone systems have allowed adjustment of temperature in each zone. However, optimum comfort depends not only on temperature but also on the volume of air flow discharged from the vent of a duct. While it has been known in a multiple passage network to include a throttle valve in one passage for adjusting the air flow through it, the adjustment is typically made at the expense of the air flow in neighboring passages; that is, the total flow is apportioned among the several passages and when the flow is decreased in one passage it is increased in the neighboring passage or vice versa. If applied to a multi-zone system, that arrangement would result in enabling one zone to be adjusted while upsetting the flow in other zones.